1. Field of the Invention
The invention relates to a heating system.
2. Related Art Statement
In a system for producing semiconductors, a ceramic heater has been provided for heating a wafer so as to deposit a semiconductor thin film on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like. Such a ceramic heater is known as a two-zone heater. Such two-zone heater has a ceramic substrate and inner and outer resistance heat generators made of a metal of a high melting point embedded in the substrate. Separate power supply terminals are connected to the respective heat generators so that electric power is applied independently to the respective generators. The inner and outer heat generators can be thus independently controlled.
According to JP-A 5-326112, a resistance heat generator of a ceramic heater is constituted by plural circuit patterns each made of a high molting point metal. The circuit patterns are so arranged that they may supplement one another's defect portions. It is provided that one of the patterns has a defect portion such as a folded portion or a returning portion. In this case, another circuit pattern is overlapped on or over the defect portion of the one pattern.
For example, in a heater to be used for heating semiconductor wafers, the temperature of the heating face of the heater needs to be uniformly controlled over the entire surface. It is required that the heater satisfies strict specifications, for example, that the temperature measured on the heating face must be held within ±10° C. of the average across the whole heating face under a use condition. A ceramic heater is excellent on the viewpoint of uniformity of temperature on the heating face. Further, for example, when a semiconductor wafer is held and heated, it is possible to reduce thermal deformation of the surface contacting a wafer over time and to preserve the flatness of a wafer.
Such ceramic heater is needed to be fixed onto an inner wall surface of a chamber. One end of a tubular substrate made of a ceramic plate is fixed to a joining face of a ceramic heater and the other end of the supporting member is fixed to an inner wall surface of a chamber. The supporting member is formed of a heat resistant ceramic plate made of alumina, aluminum nitride or the like. The supporting member and chamber are sealed with each other in an air-tight manner with an o-ring. The inner space of the supporting member and the inner space of the chamber are sealed in an air-tight manner to prevent the leakage of a gas in the inner space of the chamber to the outside of the chamber.